Abstract: A variable inlet for a marine jet propulsion system comprising a movable lip, a center splitter serving to divide said inlet into upper and lower passages and coupled for movement proportional to that of said lip to assure equality of the areas of said upper and lower passages, and apparatus for varying the outward projection of said splitter to vary the diffusion ratio of said upper and lower passages.

Abstract: A suction device for a jet propeller assembly for a boat comprises a motor actuating a pump assembly and a suction conduit conveying water to the pump assembly. The suction inlet is located aft of the boat stern transom and has a rectangular minimum height cross-section with width to height ratio of 3 to 6. Preferably the suction inlet is located entirely rearwardly of the stern transom, the minimum height cross-section plane makes a 30.degree. to 60.degree. angle with the horizontal and the distance between the forward edge of the suction inlet and the pump inlet cross-section is not greater than twice the inlet cross-section diameter. Thus the suction device can be displaceably mounted with respect to the hull, no opening in the keel of the hull is necessary and the suction conduit can be located entirely aft of the stern transom. The propeller assembly efficiency and the wake dynamics are improved.

Abstract: The invention relates to a method for producing a thrust in manoeuvering engines for watercraft and a manoeuvering engine constructed for the same, whereby the method comprises the annular driving water jet supplied to the diffuser and enveloping a first suction water jet is fed to a second suction water jet supplied to the diffuser inner wall surface, while the manoeuvering engine is constructed in such a way that the rear part of the engine casing is provided with an inlet port having a smaller diameter than the outlet port and located in the vicinity of the outlet port of the front engine part, whereby for the optimum adaptation of the exit mixing jet velocity to the vehicle speed a water jet exit cross-section regulating device is provided.

Abstract: A reversible hydrojet boat drive for the substantially nonturbulent nozzling of water during the forward mode, and effective non jamming seal function during the reverse mode, and comprised of an exact nozzle continuation of the exit passage of the pump, particularly the top wall thereof, and the compatible eccentric relation of the surrounding seals of the reverse gate centered below the axis of gate rotation, thereby to avoid jamming and to eleviate strain on the control system therefor.

Abstract: A tubular duct is provided for ship propellers with blade tips having barrier plates extending transversely therefrom. The tubular ducts are effectively arranged to extend the barrier plates in a manner which, in operation, directs a fluid stream in substantially shock-free contact with such plates.

Abstract: A hydro-jet drive for watercraft. A device is provided applicable for mounting in the hull of a boat by which a jet stream can be created and directed in any desired direction for movement of the boat accordingly. There is provided an elbow having an intake portion and a substantially horizontal discharge opening. The elbow is rotatable on an axis of rotation and contains a suitable motor driven impeller. A motor driven device is provided for rotating the elbow about the axis of rotation thereof for effecting discharge in an operator determined direction. The axis of rotation of the impeller is arranged eccentrically with respect to the axis of rotation of the elbow. The device is particularly adaptable for shallow draft vessels.

Abstract: A water jet propelled boat hull having an axis of forward motion, a bottom and a centerline. A first and a second water duct are provided, each of which has an exit port discharging rearwardly, the exit ports being laterally spaced from the centerline and on opposite sides of the centerline from each other. Inlet ports are located substantially on the centerline at the bottom of the hull. The ducts interconnect respective inlet ports and respective exit ports. A first and a second water jet propulsion device, such as a pump, is disposed respectively in each of the said first and second ducts to move water from the inlet ports and out the exit ports. Because the inlet ports are on the centerline, both ducts will be provided with water, even when the boat is inclined as a consequence of making sharp turns.

Abstract: A jet ski has a hull, a motor mounted in the hull for driving a pump in an aft section of the hull, and a well formed in the bottom of the hull in front of an opening to the pump impeller. A grating which covers the well has a scoop below and in front of an opening to the pump housing for scooping water and directing it toward the impeller during use. Water from the impeller is forced under pressure through a jet nozzle aft of the impeller for providing motive power for the hull. The scoop has a concavely curved, inclined surface with a continuous and uninterrupted bottom edge projecting below the plane of the hull bottom surface, which results in increased velocity of the ski.